This invention relates to chemically stable urea-formaldehyde forms, and more particularly to a method whereby chemical stability is increased by modification of the partially cured urea-formaldehyde resin by acid catalyzed reaction with water soluble dialdehydes and supplemental urea. The said modified resin when combined with a froth, produced by forcing air through a dilute acidic aqueous surfactant solution, after application and placement, cures and dries to a light weight contiguous foam mass having a high degree of chemical stability. Such foams are used for heat and sound insulation in commercial and residential buildings where foam stability over long periods of time is essential.
Urea-formaldehyde foams after curing and drying are relatively light weight, and possess good heat and sound insulating properties. The foams are normally applied as a wet, partially cured, fluid froth which flows into and accurately fills areas or cavities to be insulated. The prior art has reported solution to many of the problems relating to applicaton, such as production of uniform foam cell size and constant composition of the resin-curing agent blend. The excellent insulating properties, the relatively low cost, and the ease and accuracy of application are factors which should allow urea-formaldehyde foams to become a major commercial insulation material.
Unfortunately, urea-formaldehyde foams developed to date and reported in the prior art do not have the integrity required for commercial utility. Integrity is used here to indicate an ability to remain constant and unchanged throughout long periods of use as insulation. The prior art foams have lacked both physical and chemical integrity under normal use conditions. That is, the physical size, shape, contiguality, appearance, crystallinity, and the chemical composition of the urea-formaldehyde foams have changed significantly to the detriment of their insulating effectiveness. These conventionally prepared urea-formaldehyde foams, therefore, produce inferior insulation after the foams have lost their physical and chemical integrity.
Copending U.S. application, by this inventor, filed the same day as this application, discloses that the physical integrity, including physical size, shape, contiguality and appearance of urea-formaldehyde foam, may be preserved for long useful periods of time by incorporating linearly shaped refractory solid particles in the foam during application. Although preservation of the physical integrity of the foam provides a significant improvement in the utility of urea-formaldehyde foams, it does not provide a completely satisfactory insulating material, where chemical instability and degradation of the foam occurs.
Urea-formaldehyde polymers in conventional foams chemically decompose slowly under normal insulating conditions and the decomposition becomes more rapid as temperature and humidity are increased. The chemical decomposition of the foam seriously impairs the utility of the foam insulation by breaking down the cellular structure of the foam to a crystalline solid structure having little physical strength, and poor insulating properties. Objectionable odors are created by formaldehyde vapors released by the chemical degradation of the urea-formaldehyde polymers.
It is therefore a primary object of this invention to provide a method of producing a substantially chemically stable urea-formaldehyde based insulating foam.
It is another object of this invention to provide a method for modifying urea-formaldehyde resins for use in forming chemically stable insulating foams.
It is still another object of this invention to provide a method of producing a cured urea-formaldehyde insulating foam substantially free from formaldehyde vapor and odor.
These and other objects will be evident from the following description of the invention.